Sediment Characters And Major River Contribution To The West Side Nearshore Of The Taiwan Strait

A lot of sediment, sub-bottom profile and side-scan sonar data have been acquired in thewestern nearshore of the Taiwan Strait, during the marine geophysics and geology investigation in2005²009. Through data processing and analysis, combining with the¹⁴C,²¹⁰Pb data have beenpublished in the Taiwan Strait, the distribution of surface sediments, shallow strata of sedimentarysequences, and sediment flux buried in the west side nearshore of the Taiwan Strait are studied.Especially, the flux and fate of the largest rivers derived sediment into the west side of the TaiwanStrait is estimated, and the river sediment contribution to the Taiwan Strait are compared betweenwest side and the east side of the Strait.The Taiwan Strait in the Southeast Asia continent is the largest Strait in China, and is themain material and energy exchange channel between the South China Sea and East China Sea.Which dominant by West Pacific high and the Asian monsoon on the climate; the Kuroshioflows via both sides of the Taiwan Strait Island which originated from the North PacificOcean, associated with the effects of South China Sea Warm Current and the East China Seacirculation, development of upwelling, ocean front and other oceanographic processes, andmany mountain rivers delivered into the Strait from east and west side; the Taiwan Strait isalso the suture zone of continental plate and oceanic plate in geology. These charactersmaking this area are an important hub for Earth System Science between the Western Pacificand East Asia, providing a unique platform for nature study in the atmosphere, hydrosphereand geosphere.Sediment types in the west side nearshor of the Taiwan Straits are bounded by the HaitanIsland, particles size increases from north to south in the northern, the same with the southernfrom coastal to sea. A variety of sand wave developed in this area, and can be classifiedthrough shape,like deflection ripples, linear ripples, scaly ripples, and other micro-landformtypes, associated with the distribution of sand ridges.Two acoustic reflection interface are identified with QT₀and QT₁in the seismic profiles, further QT₀¹、QT₀²reflection interface can be recognition locally, and divided into Ⅰ₁、Ⅰ₂andⅠ₃acoustic units, corresponding to late holocene, middle Holocene and early Holocene.sedimentary thickness of Holocene in the western side nearshore of the Taiwan Strait isdifferences, bounded by Hai Tan Island, northern of Holocene deposition is generally greaterthan10m, there is a trend from north to south thinner, like a shape of strip in south-northdirection; while the thickness of Holocene sediment in the south of Hai Tan Island has anincreasing trend from the shore to sea. The west side nearshore sediment flux of the TaiwanStrait revealed by this study is14.3¹1.7Mt/y, a figure not too different from the threemajor rivers in the west of the Strait,as Minjiang River （7.5Mt/y）, Jiulong river（3Mt/y）,Jinjiang river（2.5Mt/y） and so the estimated total flux from river delivered into the sea about13Mt/y. But the flux from Yangtze River transport to this area as well as bed load flux fromLocal River is not consideration.Ancient channel can be divided into two branch in Min river, Jiulong river and Jinjiangriver adjacent region, such as north and south branch, but south channel of the river is oftengreater density and width than the the north branch, may be the main channel into the sea atthe time. In addition, the Minjiang River, Jiulong River can be seen a significant sedimentarycharacteristic of subaqueous delta, similar with the modern Yangtze subaqueous deltasequence by Huang Huizhen revealed. The morphology of Minjiang River and Jiulong Riversubaqueous Delta is different, the former is a narrow-south and north-width like axe, and thelatter is dumbbell-shaped.Minjiang River and Jiulong River may capture about half of the river delivered fluxwithin the estuary and subaqueous delta, the rest entered into the Taiwan Strait. However, thisestimation doesn’t consider the river bed-load material sediment discharge. Assumption thesubaqueous delta front is the main area capture of suspended load matter from Minjiang Riverand Jiulong River, then suspended sediment mass flux is estimated of about0.5Mt/y, whilethe Jiulong River delta sediments is only0.17Mt/y, far underestimate the current flux in Minriver（7.5Mt/y）and Jiulong river（3Mt/y） respectively, likely to represent a large number ofsuspended sediment particles into the Taiwan Strait.The amount of river delivered sediment from the watershed and sediment discharge per unitarea is larger in the east side of Taiwan Strait than in the west side, ex the total sediment discharge in western of Taiwan Strait is about1/10of eastern. But it is worth noting that theflux from Taiwanese river may be escape from the Taiwan Strait. A lot part of them transportto the north through the South China Sea Warm Current and Kuroshio, with the conduct of thecold eddy in the northeast of Taiwan Island; and the flux from the river of south side inTaiwan Island transport into the east-north of South China Sea through canyon and adjacentchannels. However, the majority flux from the western side river delivered sediment of theTaiwan Strait is accumulation in the strait, so its total contribution to the long-term may notbe less than the river’s west of the Strait.